Hydroxide Is Not a Promoter of C 2+ Product Formation in the Electrochemical Reduction of CO on Copper

Steering the Selectivity of CORR from Acetate to Ethanol via Tailoring the Thermodynamic Activity of Water

The electrochemical conversion of carbon monoxide (CO) into oxygenated C2+ products at high rates and selectivity offers a promising approach for the two-step conversion of carbon dioxide (CO2). However, a major drawback of the CO electrochemical reduction in alkaline electrolyte is the preference for the acetate pathway over the more valuable ethanol pathway. Recent research has shed light on the significant impact of thermodynamic water activity on the electrochemical CO2 reduction reaction pathways, but less is understood for the electrochemical reduction of CO. In this study, we investigated how the water activity at the electrified interface can be enhanced to adjust the selectivity between acetate and ethanol. We employed an ionomer modifier to lower the local concentration of alkali ions (via Donnan exclusion), successfully enhancing ethanol production while suppressing acetate formation. We observed a remarkable improvement in the Faradaic efficiency of ethanol and alcohol (i. e. ethanol, propanol etc), which reached 42.5 % and 55.1 %, respectively, at a current density of 700 mA cm-2. The partial current densities of ethanol and alcohol reached 698 and 942 mA cm-2 at 2000 mA cm-2. Furthermore, we achieved a 3.7-fold increase in the ethanol/acetate ratio, providing clear evidence of our successful modulation of product selectivity.

Rational Design of Local Reaction Environment for Electrocatalytic Conversion of CO2 into Multicarbon Products

The electrocatalytic conversion of CO2 into multi-carbon (C2+) products provides an attractive route for storing intermittent renewable electricity as fuels and feedstocks with high energy densities. Although substantial progress has been made in selective electrosynthesis of C2+ products via engineering the catalyst, rational design of the local reaction environment in the vicinity of catalyst surface also acts as an effective approach for further enhancing the performance. Here, we discuss recent advances and pertinent challenges in the modulation of local reaction environment, encompassing local pH, the choice of the species and concentrations of cations and anions as well as local reactant/intermediate concentrations, for achieving high C2+ selectivity. In addition, mechanistic understanding in the effects of the local reaction environment is also discussed. Particularly, the important progress extracted from in situ and operando spectroscopy techniques provides insights into how local reaction environment affects C-C coupling and key intermediates formation that lead to reaction pathways toward a desired C2+ product. The possible future direction in understanding and engineering the local reaction environment is also provided.

Local hydrophobicity allows high-performance electrochemical carbon monoxide reduction to C2+ products

While CO can already be produced at industrially relevant current densities via CO₂ electrolysis, the selective formation of C₂₊ products seems challenging. CO electrolysis, in principle, can overcome this barrier, hence forming valuable chemicals from CO₂ in two steps. Here we demonstrate that a mass-produced, commercially available polymeric pore sealer can be used as a catalyst binder, ensuring high rate and selective CO reduction. We achieved above 70% faradaic efficiency for C₂₊ products formation at j = 500 mA cm^-2 current density. As no specific interaction between the polymer and the CO reactant was found, we attribute the stable and selective operation of the electrolyzer cell to the controlled wetting of the catalyst layer due to the homogeneous polymer coating on the catalyst particles' surface. These results indicate that sophistically designed surface modifiers are not necessarily required for CO electrolysis, but a simpler alternative can in some cases lead to the same reaction rate, selectivity and energy efficiency; hence the capital costs can be significantly decreased.

Recent Progress in Electrochemical Nitrogen Reduction on Transition Metal Nitrides

Distributed electrochemical nitrogen reduction reaction (ENRR) powered by renewable energy for the on-site production of ammonia is an attractive alternative to the industrial Haber-Bosch process, which is responsible for roughly 2 % of global energy consumption. In this Review, we summarize recent progress in the ENRR catalyzed by transition metal nitrides (TMNs). The unique electronic structures of TMNs make them promising ENRR catalysts for active and selective ammonia production, which have been predicted theoretically and demonstrated experimentally. Reaction pathways and deactivation mechanisms of the ENRR on different TMNs are surveyed, and current understanding of structure-activity relations is discussed. To develop highly active, selective, and stable TMN catalysts for industrial-scale ENRR, membrane electrode assembly configuration is recommended in catalyst evaluation. Furthermore, we highlight the importance of developing mechanistic understanding on ENRR with different operando spectroscopic techniques.

Electrochemical CO2 reduction toward multicarbon alcohols - The microscopic world of catalysts & process conditions

Tackling climate change is one of the undoubtedly most important challenges at the present time. This review deals mainly with the chemical aspects of the current status for converting the greenhouse gas CO2 via electrochemical CO2 reduction reaction (CO2RR) to multicarbon alcohols as valuable products. Feasible reaction routes are presented, as well as catalyst synthesis methods such as electrodeposition, precipitation, or sputtering. In addition, a comprehensive overview of the currently achievable selectivities for multicarbon alcohols in CO2RR is given. It is also outlined to what extent, for example, modifications of the catalyst surfaces or the use of bifunctional compounds the product distribution is shifted. In addition, the influence of varying electrolyte, temperature, and pressure is described and discussed.

Steering the Glycerol Electro-Reforming Selectivity via Cation-Intermediate Interactions

Electro-reforming of renewable biomass resources is an alternative technology for sustainable pure H2 production. Herein, we discovered an unconventional cation effect on the concurrent formate and H2 production via glycerol electro-reforming. In stark contrast to the cation effect via forming the double layers in cathodic reactions, the presence of residual cations at the anode were discovered to interact with the glycerol oxidation intermediates to steer its product selectivity. Through a combination of product analysis, transient kinetics, crown ether trapping experiments, in situ IRRAS spectroscopy and DFT calculation, the aldehyde intermediates were discovered to be stabilized by the Li+ cations to favor the non-oxidative C-C cleavage for formate production. The maximal formate efficiency could reach 81.3% under ~ 60 mA/cm2 in LiOH. This work emphasizes the significance of engineering the microenvironment at the electrode-electrolyte interface for efficient electrolytic processes.

C-C Coupling Is Unlikely to Be the Rate-Determining Step in the Formation of C2+ Products in the Copper-Catalyzed Electrochemical Reduction of CO

The identity of the rate-determining step (RDS) in the electrochemical CO reduction reaction (CORR) on Cu catalysts remains unresolved because: 1) the presence of mass transport limitation of CO; and 2) the absence of quantitative correlation between CO partial pressure (p_CO ) and surface CO coverage. In this work, we determined CO adsorption isotherms on Cu in a broad pH range of 7.2-12.9. Together with electrokinetic data, we demonstrate that the reaction orders of adsorbed CO at p_CO <0.4 and >0.6 atm are 1^st and 0^th , respectively, for multi-carbon (C₂₊ ) products on three Cu catalysts. These results indicate that the C-C coupling is unlikely to be the RDS in the formation of C₂₊ products in the CORR. We propose that the hydrogenation of CO with adsorbed water is the RDS, and the site competition between CO and water leads to the observed transition of the CO reaction order.

Insight into Structural Evolution, Active Site and Stability of Heterogeneous Electrocatalysts

The structure-activity correlation study of electrocatalysts is essential for improving conversion from electrical to chemical energy. Recently, increasing evidences obtained by operando characterization techniques reveal that the structural evolution of catalysts caused by the interplay with electric fields, electrolytes or reactants/intermediates brings about the formation of real active sites. Hence, it is time to summarize the structural evolution-related research advances and envisage their future developments. In this minireview, we first introduce the fundamental concepts associated with structural evolution ( e.g., catalyst, active site/center and stability/lifetime) and their relevance. Then, the multiple inducements of structural evolution and advanced operando characterizations are discussed. Lastly, a brief overview of structural evolution and its reversibility in heterogeneous electrocatalysis, especially for representative electrocatalytic oxygen evolution reaction (OER) and CO 2 reduction reaction (CO 2 RR), along with key challenges and opportunities, is highlighted.